Nutrients and Their Functions

Introduction

Let's review the essential elements that the human body relies on for survival and our daily functions. Each body system has specific requirements and functions. If one of our systems fails, it will have a negative impact on all of our body systems. It's important to understand what our body needs to remain healthy.

 

Nutrients in the Body

The food we consume contains a mixture of water, protein, carbohydrates, lipids (fats), minerals, and vitamins. This is all fuel for the body—building blocks for the chemical reactions needed to run the body.

After your body digests food, it uses these building blocks to construct muscle tissue, deposit fat underneath your skin, and store carbohydrate energy. This process is called anabolism. Anabolism requires energy.

Catabolism is the opposite process, in which a complex substance is broken down into its smaller components. For example, if you exercise for a sufficient amount of time, your body will begin "burning fat" (that is, breaking it down into smaller molecules to release the necessary energy required for continued exercise).

Metabolism is the sum of the chemical reactions of anabolism and catabolism.

 

Water

Water makes up more than half of the human body. Not only does water flow through our vessels as a component of blood, it fills up the space inside and between our cells. Water is required for survival. Without water, the body is at risk for serious damage. Each body system depends on fluids to operate. We need a minimal amount of water each day to continue supporting our tissues and organs.

Drinking enough water isn't usually an issue. However, certain scenarios do require more water, such as the following:

• Vomiting and diarrhea—significant dehydration
• Prolonged exercise—loss of water through sweating
• Some crash diets—primarily water loss

 

Carbohydrates

Carbohydrates are found in starches and sugars. They're our main source of energy. All carbohydrates are eventually broken down into or converted into glucose. This molecule serves as a ready source of energy for immediate use, or it can be stored as glycogen in the muscles and liver. Your body releases glucose from these glycogen stores during exercise or short-term starvation.

 

Lipids

Lipids are known for their capability to store energy, but they also provide protection and communication between cells. There are different types of lipids, and each one serves a purpose.

• Fats and oils assist with energy storage. They're broken down and distributed when the body is in need. But in contrast to that of carbohydrates, the energy from lipids can't be used rapidly. Fat stores are designed to be used during long-term starvation.
• Waxes are lipids that work as a protection level. They help cells by preventing water loss within the body.
• Steroids are lipids that assist with the communication process between cells. Steroids are composed of cholesterol, testosterone, and estrogen.

 

Protein

Protein is the third major nutrient. Proteins aren't designed to serve as a significant energy source. Protein is the basic building block of the body. It makes up muscles and other tissues and is found in every part of our cells. All the enzymes that drive our metabolism are proteins. Antibodies of the immune system are also proteins. 

Protein is used for energy only in times of extreme stress or starvation. After carbohydrate and fat stores are consumed, the body is forced to break down protein for energy.

 

Use of protein for energy requires a costly sacrifice of structural proteins as well as those involved in enzyme pathways and the immune system. Dietary protein is broken down into amino acids.

The body can't make all the amino acids it needs. There are nine essential amino acids that must be acquired from the diet. A food is labeled as a complete protein if it contains all nine essential amino acids. Incomplete proteins don't contain all the essential amino acids.

 

Minerals, Trace Elements, and Vitamins

Minerals and trace elements are chemical compounds present in very small amounts in food. They don't contain calories, so they don't provide energy. But they do serve a variety of purposes in daily metabolism. 

Vitamins are organic compounds that function as coenzymes, assisting enzymes in catalyzing chemical reactions. Vitamin deficiencies can result in conditions specific to the metabolic pathways involved. 

 

Calories

The calorie is a measure of energy contained in food. A kilocalorie equals 1,000 calories. We tend to use kilocalories when talking about energy content. For instance, a "600 calorie burger" actually has 0.6 kilocalories.

Each individual needs a certain amount of kilocalories per day to maintain normal body function.

Carbohydrates and protein both contain four kilocalories per gram (that is, a 200-gram meal of pure carbohydrates would contain 800 kilocalories). Fat contains nine kilocalories per gram.

 

Key Points

• The food we consume contains a mixture of water, protein, carbohydrates, lipids (fats), minerals, and vitamins. This is all fuel for the body.
• Carbohydrates are our main source of energy and are found in starches and sugars.
• Lipids are known for their capability to store energy, but they also provide protection and communication between cells.
• Protein makes up muscles and other tissues and is found in every part of our cells. All the enzymes that drive our metabolism are proteins.
• Minerals and trace elements are chemical compounds present in very small amounts in food; they serve a variety of purposes in daily metabolism.
• Vitamins are organic compounds that function as coenzymes, assisting enzymes in catalyzing chemical reactions